A hearing instrument for insertion into the user's ear canal may be manufactured by fabricating the hearing instrument shell using stereo lithography (SLA), one of the processes mentioned in U.S. Patent Application Publication No. 2002/0196954 A1, published Dec. 26, 2002 and titled, “Modeling and fabrication of three-dimensional irregular surfaces for hearing instruments,” incorporated here by reference. When using SLA, a part is constructed layer by layer. Since the raw material is a liquid bath, a means of supporting the initial layers is required to prevent the piece from floating away.
Typically, a support structure is created along with the part and then later discarded (e.g., during a finishing process such as tumbling). One such support structure comprises a plurality of thin columns, perhaps braced together. When the part is finished, it is lifted out of the structure and the bath, and the support structure is discarded.
Some hearing instrument shells have receiver holes with finely detailed features. Since the receiver hole is located on the tip of the shell, it is one of the first items formed during the SLA process. Further, as the support structures are created simultaneously with the shell, these structures may extend into openings on the bottom of the shell, such as the receiver hole. Once the part is finished, extensive machining may be required to remove the support from the receiver hole and restore the hole structure.
The entry of the support structure into the receiver hole can be prevented by shielding the receiver hole with a structure such as a dome having a thin shell. Once the part is completed, the dome can be removed without harming the part.